JP2009199044A - Retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film, which has retardation suitable for a retardation film, and exhibits very excellent flexibility. <P>SOLUTION: The retardation film is mainly composed of acrylic polymer, and contains elastic organic fine particles. An in-plane retardation at a wavelength of 589 nm is 15-100 nm, the in-plane retardation in a thickness direction at the wavelength of 589 nm is 70-400 nm, and the folding endurance numbers are 100 or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a retardation film.

  In recent years, the demand for visibility (brighter, easier to see, better contrast, higher viewing angle, etc.) has become stricter as the screen size and usage environment of liquid crystal display devices (LCDs) have expanded. However, since only the improvement of the liquid crystal cell main body cannot sufficiently satisfy the demand for improving the visibility, it largely depends on the performance improvement of the optical film such as a retardation film.

  Therefore, the optical film such as a retardation film has high transparency, low photoelasticity, heat resistance, light resistance, high surface hardness, high mechanical strength, large retardation, and small wavelength dependence of retardation, Characteristics such as small dependence of the phase difference on the incident angle are required.

  On the other hand, acrylic resins (acrylic polymers) typified by PMMA are well known to have excellent optical characteristics, and various conventional optical materials having high light transmittance, low birefringence, and low retardation are known. It is applied to the use of. However, since acrylic resin has low retardation development performance, it is difficult to obtain a necessary retardation value even if it is stretched. Further, while the use environment of the liquid crystal display device becomes severe, the demand for heat resistance of the optical film has increased, but it is difficult to impart sufficient heat resistance to the stretched film of PMMA.

  Furthermore, the acrylic resin is easily cracked when formed into a film, and there is room for improvement in order to obtain mechanical strength, particularly sufficient flexibility.

  Further, studies have been made to improve heat resistance by introducing various ring structures into the acrylic resin. However, when the heat resistance is improved, the resin becomes brittle and the flexibility of the film tends to decrease.

On the other hand, as a method for improving the flexibility of an acrylic resin, it is known to stretch the film or to contain organic fine particles in the film (see, for example, Patent Documents 1 to 3).
JP 2006-257263 A (published September 28, 2006) JP 2006-241197 A (published September 14, 2006) International Publication No. 2007/099927 (published on September 7, 2007)

  However, there is a demand for a film having further improved flexibility than the configurations of Patent Documents 1 to 3 above.

  This invention is made | formed in view of said problem, The objective is to implement | achieve the phase difference film which has a phase difference suitable for a phase difference film, and is very excellent in flexibility.

  In order to solve the above-mentioned problems, the present inventor has intensively studied to further improve the flexibility of the retardation film.

  As a result, it was found that the flexibility of the retardation film was remarkably improved by sequentially biaxially stretching a film containing organic fine particles and containing organic fine particles, and the present invention was completed. It was.

  That is, the retardation film according to the present invention is a retardation film containing an elastic polymer as a main component and containing elastic organic fine particles in order to solve the above-described problems, and has an in-plane retardation value at a wavelength of 589 nm. Within a range of 15 nm to 100 nm, a retardation value in the thickness direction at a wavelength of 589 nm is within a range of 70 nm to 400 nm, a sample film having a width of 15 mm and a length of 80 mm is used, and the load is 50 g. The folding number of times measured according to JIS P8115 is 100 times or more.

  According to the said structure, there exists an effect that it has a phase difference suitable for a phase difference film, and can provide the phase difference film which is very excellent in flexibility.

  In the retardation film according to the present invention, the folding resistance is preferably 500 times or more.

  In the retardation film according to the present invention, the haze is preferably 2% or less.

  The retardation film according to the present invention is preferably obtained by biaxial stretching.

  In the retardation film according to the present invention, the elastic organic fine particles have a conjugated diene monomer structural unit constructed by polymerizing a conjugated diene monomer as an essential component, and have a low-temperature side glass transition temperature of −40. It is preferable that it is less than ° C.

  According to the above configuration, the elastic organic fine particles have a conjugated diene monomer structural unit exhibiting positive birefringence when polymerized, and the glass transition temperature on the low temperature side is less than −40 ° C. Flexibility can be further improved without significantly reducing the phase difference characteristics.

  In the retardation film according to the present invention, the elastic organic fine particles preferably have a conjugated diene monomer structure obtained by polymerizing at least one monomer selected from the group consisting of butadiene and isoprene. .

  The retardation film according to the present invention preferably has a glass transition temperature on the high temperature side in the range of 110 ° C. or higher and 200 ° C. or lower.

  According to the above configuration, the film can be used in a harsh environment while ensuring the moldability of the film, and the occurrence of unevenness in retardation due to deformation of the film can be suppressed.

  In the retardation film according to the present invention, the acrylic polymer preferably has a lactone ring structure.

  In the retardation film according to the present invention, the lactone ring structure has the following general formula (1).

(In the formula, R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.)
It is preferable that it is a structure represented by these.

  According to the said structure, phase difference performance can be improved more, without reducing heat resistance.

  The retardation film according to the present invention is a retardation film containing an acrylic polymer as a main component and containing elastic organic fine particles as described above, and an in-plane retardation value at a wavelength of 589 nm is 15 nm or more and 100 nm or less. It is within the range, the retardation value in the thickness direction at a wavelength of 589 nm is in the range of 70 nm to 400 nm, a sample film with a width of 15 mm and a length of 80 mm is used, and the load is 50 g, in accordance with JIS P8115. The number of folding times measured in this way is 100 times or more.

  For this reason, there exists an effect that it has a phase difference suitable for a phase contrast film, and can provide a phase contrast film which is very excellent in flexibility.

  An embodiment of the present invention will be described as follows.

  In the present specification, “(meth) acryl” means acryl or methacryl, and “main component” means 50% by mass or more. Further, “weight” is treated as a synonym for “mass”, and “weight%” is treated as a synonym for “mass%”. Further, “A to B” indicating a range indicates that it is A or more and B or less, and in this specification, “ppm” means a value obtained in terms of mass unless otherwise specified, for example, 10,000 ppm. Means 1% by mass.

  Further, various physical properties listed in the present specification mean values measured by the methods described in the examples described later unless otherwise specified.

  The retardation film according to the present embodiment is a retardation film containing an acrylic polymer as a main component and containing elastic organic fine particles, and an in-plane retardation value at a wavelength of 589 nm is within a range of 15 nm to 100 nm. Yes, the retardation value in the thickness direction at a wavelength of 589 nm is in the range of 70 nm to 400 nm, and the folding resistance is 100 times or more.

(I) Acrylic polymer The acrylic polymer that is the main component of the retardation film according to the present embodiment is a resin obtained by polymerizing a monomer composition containing (meth) acrylic acid ester as a main component. If there is no particular limitation. Moreover, what has 2 or more types of acrylic polymers as a main component may be sufficient.

  Examples of the (meth) acrylic acid ester include the general formula (2)

(In the formula, R ⁴ and R ⁵ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms.)
A compound (monomer) having a structure represented by the formula: acrylic acid ester such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, cyclohexyl acrylate, benzyl acrylate, etc. Methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate and benzyl methacrylate; You may use only a seed | species and may use 2 or more types together. Among these, in particular, a compound having a structure represented by the general formula (2), methyl methacrylate, is more preferable from the viewpoint of excellent heat resistance and transparency. In addition, benzyl (meth) acrylate is preferred in terms of increasing positive birefringence (positive phase difference).

  When the benzyl (meth) acrylate monomer structural unit is introduced, the preferable content of the benzyl (meth) acrylate monomer structural unit in the acrylic polymer is in the range of 5 to 50% by weight. More preferably, it is in the range of 10 to 40% by weight, and further preferably in the range of 15 to 30% by weight.

  Examples of the compound having the structure represented by the general formula (2) include methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, isopropyl 2- (hydroxymethyl) acrylate, 2- (Hydroxymethyl) normal butyl acrylate, 2- (hydroxymethyl) acrylate tertiary butyl and the like. Among these, methyl 2- (hydroxymethyl) acrylate and 2- (hydroxymethyl) ethyl acrylate are preferable, and methyl 2- (hydroxymethyl) acrylate is particularly preferable in that the effect of improving heat resistance is high. As for the compound represented by General formula (2), only 1 type may be used and 2 or more types may be used together.

  The acrylic polymer may have a structure other than the structure obtained by polymerizing the (meth) acrylic acid ester described above. The structure other than the structure obtained by polymerizing (meth) acrylic acid ester is not particularly limited, but a hydroxyl group-containing monomer, an unsaturated carboxylic acid, the following general formula (3)

(Wherein R ⁶ represents a hydrogen atom or a methyl group, X represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, an —OAc group, a —CN group, a —CO—R ⁷ group, or —C -O-R ⁸ group is represented, Ac group represents an acetyl group, R ⁷ and R ⁸ represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms.)
The polymer structural unit (repeating structural unit) constructed by polymerizing at least one selected from the monomers represented by

  Although it does not specifically limit as said hydroxyl-containing monomer, For example, allyl alcohol, such as methallyl alcohol, allyl alcohol, 2-hydroxymethyl-1-butene, (alpha) -hydroxymethylstyrene, (alpha) -hydroxyethylstyrene, 2- (Hydroxyethyl) 2- (hydroxyalkyl) acrylic acid ester such as methyl acrylate; 2- (hydroxyalkyl) acrylic acid such as 2- (hydroxyethyl) acrylic acid; and the like. Alternatively, two or more kinds may be used in combination.

  Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, α-substituted acrylic acid, α-substituted methacrylic acid and the like. These may be used alone or in combination of two or more. May be. Among these, acrylic acid and methacrylic acid are preferable in that the effects of the present invention are sufficiently exhibited.

  Examples of the compound represented by the general formula (3) include styrene, vinyl toluene, α-methyl styrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, and vinyl acetate. These may be used alone. Two or more kinds may be used in combination. Among these, styrene and α-methylstyrene are particularly preferable in that the effects of the present invention are sufficiently exhibited.

  The polymerization method is not particularly limited, and a known polymerization method can be used. A suitable method may be employed depending on the type of monomer (monomer composition) to be used, the use ratio, and the like.

  The acrylic polymer that is the main component of the retardation film according to the present embodiment has a glass transition temperature (Tg) of preferably 110 ° C to 200 ° C, more preferably 115 ° C to 200 ° C, and still more preferably 120 ° C. It is -200 degreeC, Most preferably, it is 125 degreeC-190 degreeC, Most preferably, it is 130 degreeC-180 degreeC.

  In order to enhance heat resistance, N-substituted maleimides such as phenylmaleimide, cyclohexylmaleimide, and methylmaleimide may be copolymerized, or a lactone in the molecular chain (also referred to as the main skeleton of the polymer or the main chain). A ring structure, a glutaric anhydride structure, a glutarimide structure, or the like may be introduced. Among them, a monomer that does not contain a nitrogen atom is preferable from the viewpoint of difficulty in coloring (yellowing) the film, and positive birefringence (positive phase difference) is easily expressed in the main chain. Those having a lactone ring structure are preferred.

  Regarding the lactone ring structure in the main chain, a 4- to 8-membered ring may be used, but a 5- to 6-membered ring is more preferable, and a 6-membered ring is more preferable in view of the stability of the structure. Moreover, when the lactone ring structure in the main chain is a 6-membered ring, examples include the structure represented by the general formula (1) and Japanese Patent Application Laid-Open No. 2004-168882, and a lactone ring structure is introduced into the main chain. The point of high polymerization yield in the synthesis of the previous polymer, the point that it is easy to obtain a polymer with a high content of lactone ring structure at a high polymerization yield, and (meth) acrylic acid esters such as methyl methacrylate It is preferable that it is a structure represented by General formula (1) at the point that the copolymerizability of this is good.

  When the acrylic polymer is a resin obtained by polymerizing a monomer containing a compound having a structure represented by the general formula (2), the acrylic polymer has a lactone ring structure. Is more preferable (hereinafter, an acrylic polymer having a lactone ring structure is referred to as a “lactone ring-containing polymer”). Hereinafter, the lactone ring-containing polymer will be described.

  Examples of the lactone ring structure include the following general formula (1)

(In the formula, R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.)
The structure represented by is mentioned.

  The organic residues in the general formulas (1), (2), and (3) are not particularly limited as long as they have a carbon number in the range of 1 to 20, for example, a linear or branched alkyl group. , A linear or branched alkylene group, an aryl group, an —OAc group, a —CN group and the like.

  The content of the lactone ring structure in the acrylic polymer is preferably in the range of 5 to 90% by weight, more preferably in the range of 20 to 90% by weight, and still more preferably in the range of 30 to 90% by weight. More preferably, it is in the range of 35 to 90% by weight, particularly preferably in the range of 40 to 80% by weight, and most preferably in the range of 45 to 75% by weight.

  If the content of the lactone ring structure is more than 90% by weight, the moldability becomes poor. Moreover, there exists a tendency for the flexibility of the obtained film to fall, and it is not preferable. When the content of the lactone ring structure is less than 5% by weight, it may be difficult to obtain a necessary retardation when formed into a film, and heat resistance, solvent resistance, and surface hardness may be insufficient. It is not preferable.

  In the lactone ring-containing polymer, the content ratio of the structure other than the lactone ring structure represented by the general formula (1) is that of the polymer structural unit (repeating structural unit) constructed by polymerizing (meth) acrylic acid ester. In the range of 10 to 95% by weight, more preferably in the range of 10 to 80% by weight, still more preferably in the range of 10 to 65% by weight, particularly preferably in the range of 20 to 60% by weight, Preferably it is in the range of 25 to 55% by weight.

  In the case of a polymer structural unit (repeating structural unit) constructed by polymerizing a hydroxyl group-containing monomer, it is preferably in the range of more than 0% by weight and 30% by weight or less, more preferably more than 0% by weight and 20% by weight. Within the following range, more preferably within the range of more than 0% by weight and 15% by weight or less, particularly preferably within the range of more than 0% by weight and 10% by weight or less.

  In the case of a polymer structural unit (repeating structural unit) constructed by polymerizing an unsaturated carboxylic acid, it is preferably in the range of more than 0% by weight and 30% by weight or less, more preferably more than 0% by weight and 20% by weight or less. More preferably, it is in the range of more than 0% by weight and 15% by weight or less, and particularly preferably in the range of more than 0% by weight and 10% by weight or less.

  In the case of a polymer structural unit (repeating structural unit) constructed by polymerizing the monomer represented by the general formula (3), it is preferably in the range of more than 0% by weight and 30% by weight or less, more preferably 0. It is in the range of more than 20% by weight and more preferably 20% by weight or less, more preferably in the range of more than 0% by weight and 15% by weight, particularly preferably in the range of more than 0% by weight and 10% by weight.

  The acrylic polymer described above can be obtained by performing a polymerization reaction of the monomer component including the monomer described above using a conventionally known polymerization method.

  Specifically, the lactone ring structure is obtained, for example, after obtaining a polymer having a hydroxyl group and an ester group in a molecular chain by a polymerization step as described in International Publication No. 2007/099927 pamphlet. It can introduce | transduce by heat-processing the obtained polymer.

  The lactone ring-containing polymer has a weight average molecular weight of preferably in the range of 1,000 to 2,000,000, more preferably in the range of 5,000 to 1,000,000, and still more preferably 10,000. It is in the range of ˜500,000, particularly preferably in the range of 50,000 to 500,000.

  The lactone ring-containing polymer preferably has a weight loss rate of 150% to 300 ° C in dynamic TG measurement of 1% or less, more preferably 0.5% or less, and still more preferably 0.3% or less. is there.

  Since the lactone ring-containing polymer has a high cyclization condensation reaction rate, the disadvantage that bubbles and silver streaks enter the film after molding can be avoided. Furthermore, since the lactone ring structure is sufficiently introduced into the polymer due to a high cyclization condensation reaction rate, the obtained lactone ring-containing polymer has sufficiently high heat resistance.

  The lactone ring-containing polymer preferably has a coloring degree (YI) in a 15% by weight chloroform solution of 6 or less, more preferably 3 or less, still more preferably 2 or less, and most preferably 1 or less. If the coloring degree (YI) exceeds 6, transparency may be impaired due to coloring, and it may not be used for the intended purpose.

  The lactone ring-containing polymer preferably has a 5% weight loss temperature in thermogravimetric analysis (TG) of 330 ° C. or higher, more preferably 350 ° C. or higher, and still more preferably 360 ° C. or higher. The 5% weight loss temperature in thermogravimetric analysis (TG) is an indicator of thermal stability, and if it is less than 330 ° C., sufficient thermal stability may not be exhibited.

  The lactone ring-containing polymer has a glass transition temperature (Tg) of preferably 110 ° C to 200 ° C, more preferably 115 ° C to 200 ° C, still more preferably 120 ° C to 200 ° C, and particularly preferably 125 ° C to 190 ° C. Most preferably, it is 130 to 180 ° C.

  The total amount of residual volatile components contained in the lactone ring-containing polymer is preferably 1500 ppm or less, more preferably 1000 ppm or less. If the total amount of residual volatile components is more than 1500 ppm, it may cause coloring due to deterioration during molding, foaming, or molding defects such as silver streak.

  The lactone ring-containing polymer has a total light transmittance of 85% or more, more preferably 90% or more, still more preferably, of a molded product obtained by injection molding, measured by a method according to ASTM-D-1003. Is 91% or more. The total light transmittance is a measure of transparency, and if it is less than 85%, the transparency is lowered and there is a possibility that it cannot be used for the intended purpose.

(II) Elastic organic fine particles The elastic organic fine particles (hereinafter referred to as “organic fine particles”) are those having an effect of improving physical properties of an acrylic polymer such as flexibility (bending resistance). There is no particular limitation.

  In order to have the effect of improving the flexibility of the acrylic polymer, it is more preferable that the organic fine particles have a crosslinked structure.

  The organic fine particles having a crosslinked structure can be obtained, for example, by polymerizing a monomer composition containing a polyfunctional compound having two or more nonconjugated double bonds (conjugated dienes) per molecule. .

  Examples of the polyfunctional compound include butadiene, isoprene, divinylbenzene, allyl methacrylate, allyl acrylate, dicyclopentenyl methacrylate, dicyclopentenyl acrylate, 1,4-butanediol dimethacrylate, ethylene glycol dimethacrylate , Triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl maleate, divinyl adipate, divinylbenzene ethylene glycol dimethacrylate, divinylbenzene ethylene glycol diacrylate, diethylene glycol dimethacrylate , Diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, trimethylolpropane trimethacrylate, trimethylol pro Intritriacrylate, tetramethylol methane tetramethacrylate, tetramethylol methane tetraacrylate, dipropylene glycol dimethacrylate, dipropylene glycol diacrylate, etc. It may be used in combination of two or more.

  More preferably, the elastic organic fine particles have a conjugated diene monomer structure obtained by polymerizing at least one monomer selected from the group consisting of butadiene and isoprene. The organic fine particles preferably have a glass transition temperature on the low temperature side of less than −40 ° C.

  The organic fine particles may have a structure other than a structure obtained by polymerizing the polyfunctional compound (hereinafter referred to as a structure derived from the polyfunctional compound). The structure other than the structure derived from the polyfunctional compound is represented by (meth) acrylic acid ester, hydroxyl group-containing monomer, unsaturated carboxylic acid, and general formula (3) that constitute the above-described acrylic polymer. It is preferable to have a structure of a polymer structural unit (repeating structural unit) constructed by polymerizing at least one selected from the following monomers.

  Since the organic fine particles have the structure of the polymer structural unit constituting the acrylic polymer, the dispersibility of the organic fine particles in the acrylic polymer is improved and the transparency of the film is improved. In addition, it is possible to further suppress by-product formation of foreign matters caused by aggregation of organic fine particles. Thereby, the filtration process at the time of retardation film shaping | molding can be performed in a short time.

  The organic fine particles exhibit crosslinking elasticity when obtained by polymerizing a monomer composition containing the polyfunctional compound. Thereby, the flexibility of the molded retardation film is improved, and a retardation film having excellent film moldability and bending resistance can be obtained.

  The organic fine particles are composed of a core part and a shell part obtained by further polymerizing (meth) acrylic acid ester as a shell part to a particulate polymer that becomes a core part within an average particle diameter of 0.01 μm to 1 μm. Organic fine particles having a multilayer structure, wherein the weight ratio of the core part to the shell part is in the range of 20:80 to 80:20, and the shell part is in the range of 5 wt% to 50 wt%. It is preferable that the structural unit of the monomer of 2- (hydroxymethyl) acrylic acid ester of the inside is included. Since the organic fine particles have a core / shell structure, they can be more uniformly dispersed in the acrylic polymer. Further, the organic fine particles according to the present embodiment are organic fine particles having a crosslinked structure having an average particle diameter in the range of 0.01 μm to 1 μm, and in the range of 1% by weight to 100% by weight. It preferably contains a structural unit of a monomer of (hydroxymethyl) acrylate.

  As said 2- (hydroxymethyl) acrylic acid ester, the compound which has a structure represented by General formula (2) mentioned above is preferable, and 2- (hydroxymethyl) methyl acrylate is more preferable.

  The organic fine particle has a structure derived from a polyfunctional compound only in the central part (core), and the part surrounding the central part (shell) is compatible with the acrylic polymer constituting the retardation film. It is preferable to have a high structure. As a result, the organic fine particles can be more uniformly dispersed in the acrylic polymer, and by-products of foreign matters caused by aggregation of the organic fine particles can be further suppressed. Thereby, the filtration process at the time of retardation film shaping can be performed in a shorter time. The organic fine particles having such a core-shell structure are, for example, the above-mentioned (meth) acrylic acid esters with the reactive functional group (double bond) left unreacted during the polymerization of the organic fine particles as a graft crossing point. , A hydroxyl group-containing monomer, an unsaturated carboxylic acid, and at least one selected from monomers represented by the general formula (3) can be obtained by graft polymerization. Hereinafter, the shell part and the core part of the core-shell structure will be described.

  The shell portion is not particularly limited as long as the shell portion has a high compatibility with the acrylic polymer constituting the retardation film. As a structure which comprises the shell part which has a structure with high compatibility with the acrylic polymer which comprises retardation film, when an acrylic polymer is a lactone ring containing polymer mentioned above, for example, 2- (hydroxy Methyl) a structure constructed by polymerizing a monomer composition consisting of methyl acrylate (hereinafter referred to as MHMA) and methyl methacrylate (hereinafter referred to as MMA) (hereinafter referred to as MHMA / MMA structure), A structure constructed by polymerizing a monomer composition comprising cyclohexyl methacrylate (hereinafter referred to as CHMA) and MMA (hereinafter referred to as CHMA / MMA structure), benzyl methacrylate (hereinafter referred to as BzMA), and A structure constructed by polymerizing a monomer composition comprising MMA (hereinafter referred to as a BzMA / MMA structure), methacrylic acid-2-hydroxyethyl (Hereinafter referred to as HEMA) and a structure constructed by polymerizing a monomer composition composed of MMA (hereinafter referred to as HEMA / MMA structure), acrylonitrile (hereinafter referred to as AN) and styrene (hereinafter referred to as St). And the like (hereinafter referred to as AN / St structure) and the like.

  When the shell part has an MHMA / MMA structure, the ratio of MHMA to MMA is preferably in the range of 5:95 to 50:50, and more preferably in the range of 10:90 to 40:60. preferable. Within the above range, the compatibility with the lactone ring-containing polymer is good, and the organic fine particles can be uniformly dispersed in the lactone ring-containing polymer. In addition, in the case of the shell having the MHMA / MMA structure, it preferably includes a lactone ring structure. The lactone ring structure can be introduced by forming a shell and then lactonizing.

  When the shell has a CHMA / MMA structure, the ratio of CHMA to MMA is preferably in the range of 5:95 to 50:50, and more preferably in the range of 10:90 to 40:60. preferable. Within the above range, the compatibility with the lactone ring-containing polymer is good, and the organic fine particles can be uniformly dispersed in the lactone ring-containing polymer.

  When the shell has a BzMA / MMA structure, the ratio of BzMA and MMA is preferably in the range of 10:90 to 60:40, and more preferably in the range of 20:80 to 50:50. preferable. Within the above range, the compatibility with the lactone ring-containing polymer is good, and the organic fine particles can be uniformly dispersed in the lactone ring-containing polymer.

  When the shell has a HEMA / MMA structure, the ratio of HEMA to MMA is preferably in the range of 2:98 to 50:50, and more preferably in the range of 5:95 to 40:60. preferable. Within the above range, the compatibility with the lactone ring-containing polymer is good, and the organic fine particles can be uniformly dispersed in the lactone ring-containing polymer.

  When the shell has an AN / St structure, the ratio of AN to St is preferably in the range of 5:95 to 50:50, and more preferably in the range of 10:90 to 40:60. preferable. Within the above range, the compatibility with the lactone ring-containing polymer is good, and the organic fine particles can be uniformly dispersed in the lactone ring-containing polymer.

  In particular, when the acrylic polymer is the lactone ring-containing polymer described above, it exhibits positive birefringence (positive phase difference), and therefore it is difficult to reduce the positive birefringence. In the case where the shell having the BzMA / MMA structure or the MHMA / MMA structure is further a shell having the MHMA / MMA structure, the shell preferably contains a lactone ring structure.

  The core part is not particularly limited as long as it is a structure that exhibits the effect of improving the flexibility of the acrylic polymer constituting the retardation film, and examples thereof include a structure having cross-linking. Moreover, as a structure which has bridge | crosslinking, it is preferable that it is a crosslinked rubber structure.

  The cross-linked rubber structure is a rubber having elasticity by cross-linking between main chains of a polymer having a glass transition point in the range of −100 ° C. to 25 ° C. with a polyfunctional compound. Means the structure. Examples of the crosslinked rubber structure include structures of acrylic rubber, polybutadiene rubber, and olefin rubber (repeating structural unit).

  As a structure which has the said bridge | crosslinking, the structure derived from the polyfunctional compound mentioned above is mentioned, for example. Among the polyfunctional compounds, butadiene, isoprene, 1,4-butanediol dimethacrylate, diethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, divinylbenzene, allyl methacrylate, allyl acrylate, and dicyclopentenyl methacrylate are more preferable. .

  The amount of the polyfunctional monomer used in the production of the core part is preferably within the range of 0.01 to 15% by weight of the monomer composition used, and is within the range of 0.1 to 10% by weight. More preferably, it is within. By using a polyfunctional monomer within the above range, the resulting film exhibits good folding resistance.

  The ratio of the core part to the shell part is preferably in the range of 20:80 to 80:20, more preferably in the range of 40:60 to 60:40, as the core: shell ratio by weight. If the core portion is less than 20% by weight, the bending resistance of the film formed from the organic fine particles obtained tends to deteriorate, and if it exceeds 80% by weight, the hardness and formability of the film tend to decrease.

  The core part may or may not have a cross-linked structure. Similarly, the shell part may or may not have a cross-linked structure, but only the core part. It is more preferable that has a cross-linked structure and the shell portion does not have a cross-linked structure.

  The average particle size of the organic fine particles is preferably in the range of 0.01 to 1 μm, more preferably in the range of 0.03 to 0.5 μm, and in the range of 0.05 to 0.3 μm. It is particularly preferred. When the average particle size is less than 0.01 μm, there is a tendency that sufficient flexibility cannot be obtained when a film is produced. When the average particle size exceeds 1 μm, it is used as a filter in a filtration process during film production. There is a tendency to become clogged with organic fine particles. The particle size of the organic fine particles can be measured using a commercially available particle size distribution measuring device (for example, a particle size distribution measuring device (Submicron Particle Sizer NICOMP380) manufactured by NICOMP).

  The content ratio of the organic fine particles in the retardation film according to the present embodiment is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, and further preferably 15 to 30% by weight. If the content ratio of the elastic organic fine particles is less than 5% by weight, desired flexibility may not be obtained. In addition, when the content ratio of the elastic organic fine particles exceeds 50% by weight, the transparency may decrease due to aggregation of the elastic organic fine particles, or by-products of foreign matter may increase, and the retardation film may not be used. .

  The method for producing the organic fine particles is not particularly limited. For example, conventionally known emulsion polymerization method, emulsion-suspension polymerization method, suspension polymerization method, bulk weight as described in International Publication No. 2007/099927 pamphlet. The organic fine particles can be produced by polymerizing the above-described monomer composition in a single stage or multiple stages by a combination method or a solution polymerization method. Among these, the emulsion polymerization method is more preferable.

  In addition, the organic fine particle mentioned above may be contained in the retardation film only by 1 type, and may be contained 2 or more types.

(III) Ingredients other than the acrylic polymer The retardation film according to the present embodiment may contain organic fine particles as a main component of the acrylic polymer, and may further contain other components. Good.

  Examples of the other components include olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, and poly (4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl resins; Styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer; polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate; nylon 6, Polyamide such as nylon 66 and nylon 610; polyacetal; polycarbonate; polyphenylene oxide; polyphenylene sulfide; polyether ether ketone; polysulfone; Hong; polyoxyethylene benzylidene alkylene; polyamideimide; etc. polymers.

  The retardation film may contain other additives. Examples of other additives include hindered phenol-based, phosphorus-based and sulfur-based antioxidants; light-resistant stabilizers, weather-resistant stabilizers, heat-stabilizers, and other stabilizers; reinforcing materials such as glass fibers and carbon fibers. UV absorbers such as phenyl salicylate, (2,2′-hydroxy-5-methylphenyl) benzotriazole, 2-hydroxybenzophenone; near infrared absorbers; tris (dibromopropyl) phosphate, triallyl phosphate, antimony oxide Flame retardants such as: antistatic agents such as anionic, cationic and nonionic surfactants; colorants such as inorganic pigments, organic pigments and dyes; organic fillers and inorganic fillers; resin modifiers; Inorganic fillers; plasticizers; lubricants; antistatic agents; flame retardants;

  When the retardation film contains the other additives, the content is preferably more than 0 wt% and 5 wt% or less, more preferably more than 0 wt% and 2 wt% or less, More preferably, it is in the range of more than 0% by weight and 0.5% by weight or less.

(IV) Retardation film The retardation film according to the present embodiment has (a) an in-plane retardation value at a wavelength of 589 nm in a range of 15 nm to 100 nm, and (b) a thickness direction position at a wavelength of 589 nm. The phase difference value is in the range of 70 nm to 400 nm, and (c) the folding endurance is 100 times or more.

Here, the “phase difference value” is also referred to as a retardation value. The internal phase difference value (Re) here is
Re = (nx−ny) × d
The thickness direction retardation value (Rth) is
Rth = [(nx + ny) / 2−nz] × d
Defined. Nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the direction perpendicular to nx in the film plane, nz is the refractive index in the film thickness direction, and d is the film thickness (nm). To express. The slow axis direction is a direction in which the refractive index in the film plane is maximum. Further, a material having a large refractive index in the stretching direction is said to have positive birefringence, and a material having a large refractive index in the direction perpendicular to the stretching direction in the film plane is said to have negative birefringence.

The “in-plane retardation value at a wavelength of 589 nm per thickness of 100 μm” is a value at d = 100 × 10 ³ nm in the above equation for obtaining the in-plane retardation value (Re). Further, the above-mentioned “phase difference value in the thickness direction at a wavelength of 589 nm per 100 μm thickness” refers to the value at d = 100 × 10 ³ nm in the above equation for obtaining the retardation value (Rth) in the thickness direction. That is.

(A) In-plane retardation value at wavelength 589 nm The retardation film has an in-plane retardation value (Re) at a wavelength of 589 nm in the range of 15 to 100 nm. More preferably, it is 30-90 nm.

  If the inner surface retardation value is within the above range, it can be suitably used as an optical compensation film for a VA (vertical alignment) liquid crystal display device.

  The retardation film preferably has an in-plane retardation value within a range of 5 to 1000 nm at a wavelength of 589 nm per 100 μm thickness, and more preferably within a range of 15 to 500 nm. More preferably, it exists in the range of 30-450 nm.

  If the in-plane retardation value at a wavelength of 589 nm per 100 μm thickness is smaller than 5 nm, it is not preferable because the film becomes thick to obtain a desired retardation value (retardation value). On the other hand, if the thickness exceeds 1000 nm, the retardation value (retardation value) changes with a slight change in the stretching conditions, and it may be difficult to produce stably. Furthermore, in order to obtain a large retardation value, it is necessary to increase the stretching ratio and lower the stretching temperature, and the film may be broken during the stretching process, making it difficult to produce stably. is there.

  As will be described later, the inner surface retardation value can be adjusted within the above range, for example, by successively biaxially stretching the film under a predetermined condition.

(B) Thickness direction retardation value at a wavelength of 589 nm The retardation film has a retardation value (Rth) in the thickness direction at a wavelength of 589 nm in the range of 70 nm to 400 nm. More preferably, it is 90-300 nm.

  If the retardation value in the thickness direction is within the above range, it can be suitably used as an optical compensation film for a VA liquid crystal display device.

  In the retardation film according to the present embodiment, the absolute value of the retardation value in the thickness direction at a wavelength of 589 nm per 100 μm thickness is preferably in the range of 70 to 2000 nm. More preferably, it exists in the range of 90-1500 nm.

  The retardation value in the thickness direction can be adjusted within the above range, for example, by sequentially biaxially stretching the film under a predetermined condition, as will be described later.

(C) Number of folding times The number of folding times means specifically a value measured by the method described in the examples described later.

  The retardation film has a folding resistance of 100 times or more. More preferably, it is 500 times or more.

  As will be described later, the folding resistance can be adjusted within the above range, for example, by sequentially biaxially stretching the film under a predetermined condition.

(D) Haze Preferably, the retardation film has a haze of 2% or less. More preferably, it is 1% or less. When the haze exceeds 2%, the transparency is lowered and it is not suitable as a retardation film.

  The haze can be adjusted by changing the stretching temperature during biaxial stretching of the retardation film.

(E) Other Physical Properties The thickness of the retardation film according to this embodiment is preferably 5 to 350 μm, more preferably 20 to 200 μm, and still more preferably 30 to 150 μm. When the film thickness is less than 5 μm, the strength is poor, and it is difficult to obtain a desired retardation value (retardation value). If the film thickness is larger than 350 μm, it is disadvantageous for thinning the liquid crystal display device.

  The thickness of the film can be measured using a commercially available measuring instrument such as a Digimatic micrometer (manufactured by Mitutoyo Corporation).

  Whether the birefringence is positive or negative is determined by using a polarizing microscope described in “Introduction to Polarizing Microscopes for Polymer Materials” (Hiroshi Hiroya, Agne Technical Center Edition, Chapter 5, pp 78-82 (2001)). The determination can be performed by the additive color determination method using a / 4 plate. Further, the retardation film itself or the retardation film can be heated and shrunk and then uniaxially stretched to determine whether or not the refractive index in the stretching direction is increased.

  The retardation film according to the present embodiment preferably has a glass transition temperature of 110 ° C to 200 ° C. More preferably, it is 115 degreeC-200 degreeC, More preferably, it is 120 degreeC-200 degreeC, Especially preferably, it is 125 degreeC-190 degreeC, Most preferably, it is 130 degreeC-180 degreeC. When the temperature is less than 110 ° C., the heat resistance is insufficient with respect to the harsh use environment, and the film may be deformed to easily cause unevenness in retardation, which is not preferable. Further, if it exceeds 200 ° C., it becomes an ultra-high heat-resistant retardation film, but it is not preferable because the molding processability for obtaining the film may be poor or the flexibility of the film may be greatly reduced. .

  In this specification, the glass transition temperature (Tg) is determined by the midpoint method according to ASTM-D-3418.

  The retardation film according to the present embodiment preferably has a total light transmittance of 85% or more. More preferably, it is 90% or more, More preferably, it is 91%. The total light transmittance is a measure of transparency, and if it is less than 85%, the transparency is lowered and it is not suitable as a retardation film.

  In addition to the use of the retardation film according to the present embodiment alone, it is possible to further control the optical characteristics by using it by laminating with the same kind of optical material and / or different kind of optical material. Although it does not specifically limit as an optical material laminated | stacked in this case, For example, a polarizing plate, the stretched orientation film made from a polycarbonate, the stretched orientation film made from cyclic polyolefin, etc. are mentioned.

  The retardation film according to the present embodiment is suitably used as an optical compensation member for a liquid crystal display device. Specifically, for example, retardation films for LCD such as STN type LCD, TFT-TN type LCD, OCB type LCD, VA type LCD, IPS type LCD; optical compensation film; laminated film with polarizing plate; polarizing plate optical Examples include compensation films. Moreover, the use which applied the retardation film which concerns on this Embodiment is not restrict | limited to these.

  In addition, the retardation film according to the present embodiment is used as a polarizer protective film used for a polarizing plate for a liquid crystal display device, and can be particularly preferably used as a retardation film corresponding to various liquid crystal modes. The preferable optical characteristics of the retardation film according to this embodiment vary depending on the liquid crystal mode.

  When used as a retardation film in a VA type LCD, when compensation is performed on one side of a liquid crystal cell, the in-plane retardation value at a wavelength of 589 nm is in the range of 40 to 100 nm, and the thickness direction at a wavelength of 589 nm is used. Is preferably in a range of 160 to 300 nm, an in-plane retardation value at a wavelength of 589 nm is 45 to 80 nm, and a thickness direction retardation value at a wavelength of 589 nm is further 170 to 250 nm. preferable.

  On the other hand, when it is used on both sides of a liquid crystal cell as an optical compensation film of a VA LCD and compensated with two identical optical compensation films, the in-plane retardation value at a wavelength of 589 nm is in the range of 20 to 100 nm, and The thickness direction retardation value at a wavelength of 589 nm is preferably in the range of 100 to 200 nm, the in-plane retardation value at a wavelength of 589 nm is from 25 to 80 nm, and the thickness direction retardation value at a wavelength of 589 nm is from 100 to More preferably, it is 150 nm.

(F) Method for producing retardation film The retardation film according to the present embodiment satisfying at least the above (a) to (c) includes, for example, an acrylic polymer as a main component, elastic organic fine particles, and, if necessary. It can be obtained by mixing other polymers and other additives with a conventionally known mixing method, forming into a film, and biaxial stretching such as sequential biaxial stretching and simultaneous biaxial stretching. .

  Examples of the film forming method include known film forming methods such as a solution casting method (solution casting method), a melt extrusion method, a calendar method, and a compression molding method. Among these, the solution casting method (solution casting method) and the melt extrusion method are preferable.

  Solvents used in the solution casting method (solution casting method) include, for example, chlorinated solvents such as chloroform and dichloromethane; aromatic solvents such as toluene, xylene, benzene, and mixed solvents thereof; methanol, ethanol, and isopropanol , N-butanol, 2-butanol and the like alcohol solvents; methyl cellosolve, ethyl cellosolve, butyl cellosolve, dimethylformamide, dimethyl sulfoxide, dioxane, cyclohexanone, tetrahydrofuran, acetone, ethyl acetate, diethyl ether; These solvents may be used alone or in combination of two or more.

  Examples of the apparatus for performing the solution casting method (solution casting method) include a drum casting machine, a band casting machine, and a spin coater.

  Examples of the melt extrusion method include a T-die method and an inflation method, and the film forming temperature at that time is preferably 150 to 350 ° C., more preferably 200 to 300 ° C.

  In addition, a mixture of the acrylic polymer, the elastic organic fine particles, and, if necessary, other polymers and other additives are melt-extruded from a T-die or the like, and at least one surface of the obtained film is rolled. Alternatively, a method of forming a film by contacting with a belt is preferable in that a film having a good surface property can be obtained. Furthermore, from the viewpoint of improving the surface smoothness and surface gloss of the film, a method of forming a film by bringing both surfaces of a film-like product obtained by melt extrusion molding the above mixture into contact with the roll surface or belt surface is preferred.

  In addition, although the said roll may be called a "touch roll" or a "cooling roll", the term "roll" in this specification includes both these meanings.

  Here, the temperature of the film-like material when both surfaces of the film-like material are first brought into contact with the roll or belt surface is a temperature equal to or higher than the glass transition temperature of the film-like material, preferably about 20 ° C. above the glass transition temperature. This is a high temperature.

  As the material of the roll or belt surface, metal is preferable because of good cooling efficiency and easy to obtain a film having excellent smoothness. Specific examples include stainless steel and steel. In the case of using steel, the surface thereof may be subjected to a treatment such as chrome plating. Further, the roll is preferably one having a mirror surface.

  The temperature of the roll or belt surface at the time of contacting with the film-like material is not particularly limited, but is preferably maintained at a constant temperature from the viewpoint that it can be easily formed into a film.

  The number of the rolls used is not particularly limited, but it is desirable to use 3 to 4 rolls and adjust the film thickness and surface state in multiple stages.

  The contact with the roll surface or the belt surface may be performed stepwise by contacting one surface of the film-like material and then contacting the other surface, but it is preferable to contact both surfaces simultaneously.

  The film thus obtained has sufficient thickness accuracy and surface smoothness, but in order to further improve the thickness accuracy and surface smoothness, both surfaces or one surface thereof are in contact with the roll surface or belt surface. You may heat in the state made to cool, and it may cool in the state which contacted the roll surface or the belt surface.

  In addition, in this embodiment, it is more preferable to pre-dry film raw materials, such as an acrylic polymer to be used, before forming into a film. The preliminary drying is performed using, for example, a hot air dryer or the like in the form of pellets or the like. Pre-drying is very useful because it can prevent foaming of the extruded resin.

  Moreover, it is preferable to supply the film raw material heated and melted in the extruder to the T die through a gear pump or a filter. The use of the gear pump is very useful because it has a high effect of improving the uniformity of the extrusion amount of the resin and reducing thickness unevenness. The use of the filter is useful for removing a foreign substance in the resin and obtaining a film having a defect-free appearance.

  Furthermore, when a film-like material extruded from a T die or the like is sandwiched between two rolls and cooled to form a film, one of the two rolls is a rigid metal roll having a smooth surface, The other is particularly preferably a flexible roll provided with an elastically deformable metal elastic outer cylinder having a smooth surface.

  By sandwiching a film-like material extruded from a T-die or the like with a rigid roll and a flexible roll and cooling to form a film, fine irregularities on the surface and die lines are corrected, and the surface is smooth. A film having a thickness unevenness of 5 μm or less can be obtained.

  Here, when a sheet-like molten resin extruded from a T-die or the like is cooled while being sandwiched between a rigid roll and a flexible roll to form a thin film, one roll is elastically deformable. Even so, since any roll surface is made of metal, the roll surfaces come into contact with each other, and the outer surface of the roll is easily damaged. Moreover, the roll itself is easily damaged. Therefore, when forming by such a method, the thickness of the film is preferably 10 μm or more, more preferably 50 μm or more, still more preferably 80 μm or more, and particularly preferably 100 μm or more.

  In addition, when a film having a large thickness is formed by cooling a film-like material extruded from a T-die or the like while sandwiching it between a rigid roll and a flexible roll, the cooling of the film is likely to be uneven and optical Characteristics tend to be uneven. Therefore, when it shape | molds by such a method, it is preferable that the thickness of a film shall be 300 micrometers or less, More preferably, it is 200 micrometers or less, More preferably, it is 170 micrometers or less.

  As the stretching method for obtaining the retardation film, sequential biaxial stretching and simultaneous biaxial stretching are possible in that it is easy to achieve both bending resistance in an in-plane arbitrary direction and a large in-plane retardation value. Of these, sequential biaxial stretching is preferred. Examples of the two orthogonal directions in the plane include a direction parallel to the slow axis in the film plane and a direction orthogonal to the slow axis in the film plane. In addition, what is necessary is just to set extending | stretching conditions, such as a draw ratio, extending | stretching temperature, and an extending | stretching speed suitably according to a desired phase difference value and desired bending resistance, and there is no limitation in particular.

  The sequential biaxial stretching method is not particularly limited, but any conventionally known stretching method may be employed for longitudinal stretching of sequential stretching, and examples thereof include zone stretching and roll longitudinal stretching. The zone stretching method is longitudinal uniaxial stretching having a heating zone between two nip rolls, and the roll longitudinal stretching method rotates the roll on the outlet side from the roll speed on the inlet side between the stretching rolls set to a predetermined temperature. This is a method of stretching by increasing the number.

  For transverse stretching of sequential biaxial stretching, any conventionally known stretching method may be employed, and examples include tenter stretching. Tenter stretching is performed by holding the end in the width direction of the film with a tenter clip, and moving the tenter clip holding the end in the width direction of the film along the tenter rail installed so as to gradually open the gap. Is a method of transverse stretching.

  Examples of the stretching apparatus include a roll stretching machine, a tenter-type stretching machine, and a small experimental stretching apparatus such as a tensile tester and a sequential biaxial stretching machine. The retardation film according to the embodiment can be obtained.

  The stretching temperature is preferably near the glass transition temperature on the high temperature side of the unstretched film (that is, the glass transition temperature derived from the acrylic polymer). Specifically, it is preferably performed at (high temperature side glass transition temperature −10) ° C. to (high temperature side glass transition temperature + 40) ° C. If the temperature is lower than (high temperature side glass transition temperature −10) ° C., a sufficient draw ratio cannot be obtained, which is not preferable. When the temperature is higher than (high temperature side glass transition temperature + 40) ° C., resin flow occurs, and stable stretching cannot be performed.

  The draw ratio defined by the area ratio is preferably in the range of 1.1 to 25 times, more preferably in the range of 1.2 to 10 times, and still more preferably in the range of 1.3 to 5 times. If it is smaller than 1.1 times, it is not preferable because it does not lead to the development of retardation performance accompanying to stretching and the improvement of toughness. If it is larger than 25 times, the effect of only increasing the draw ratio is not recognized.

  In the case of stretching in a certain direction, the stretching ratio for the one direction is preferably in the range of 1.05 to 10 times, more preferably in the range of 1.1 to 5 times, and still more preferably in the range of 1.2 to 3 times. Done. If it is smaller than 1.05 times, a desired phase difference value may not be obtained, which is not preferable. When it is larger than 10 times, the effect of only increasing the draw ratio is not recognized, and the film may be broken during the drawing, which is not preferable.

  The stretching speed (one direction) is preferably in the range of 10 to 20000% / min, more preferably in the range of 100 to 10000% / min. If it is slower than 10% / min, it takes time to obtain a sufficient draw ratio, and the production cost is increased, which is not preferable. If it is faster than 20000% / min, the stretched film may be broken, which is not preferable.

  The retardation film according to the present embodiment is obtained by stretching a film containing an acrylic polymer as a main component and containing organic fine particles (hereinafter sometimes referred to as “unstretched film”), The first step of stretching the glass transition temperature on the high temperature side of the unstretched film from −10 ° C. to the glass transition temperature of the high temperature side of the film + 40 ° C., and the high temperature side of the film performed after the first step It is more preferable to produce the film by stretching it by a method including a second stage step of stretching in a temperature range of from −10 ° C. to a glass transition temperature on the high temperature side of the film + 40 ° C.

  The stretching temperature in the first step is not particularly limited as long as the glass transition temperature on the high temperature side of the unstretched film is −10 ° C. or higher, but the glass transition temperature on the high temperature side of the film is −5 ° C. The glass transition temperature on the high temperature side of the film is more preferably in the temperature range of + 30 ° C., more preferably the glass transition temperature on the high temperature side of the film to the glass transition temperature on the high temperature side of the film + 20 ° C. .

  In the above description, the stretching temperature may be expressed as a temperature difference with respect to the glass transition temperature on the high temperature side of the unstretched film. In this case, for example, “the glass transition temperature on the high temperature side + 40 ° C.” is 40 ° C. higher than the glass transition temperature on the high temperature side, and “the glass transition temperature −10 ° C. on the high temperature side” is higher than the glass transition temperature on the high temperature side. Also means a temperature 10 ° C. lower.

  The draw ratio of the first step is preferably in the range of 1.1 to 25 times, more preferably in the range of 1.2 to 10 times, and still more preferably in the range of 1.3 to 5 times. Is within. When the draw ratio is lower than 1.1 times, the degree of improvement in flexibility is small, and when the draw ratio is higher than 25 times, the effect of increasing the draw ratio is reduced. There is a tendency for breakage to occur easily.

  The stretching speed in the first step is preferably in the range of 10 to 20000% / min, and more preferably in the range of 100 to 10000% / min. If the stretching speed is slower than 10% / min, it takes time to perform stretching, resulting in an increase in production cost. If the stretching speed is faster than 20000% / min, the stretched film may be broken.

  The stretching temperature in the second step is not particularly limited as long as the glass transition temperature on the high temperature side of the unstretched film is -10 ° C or higher, but the glass transition temperature on the high temperature side of the film is from -5 ° C to 5 ° C. The glass transition temperature on the high temperature side of the film is more preferably in the temperature range of + 30 ° C., and the glass transition temperature on the high temperature side of the film to the glass transition temperature on the high temperature side of the film + 20 ° C. preferable.

  The draw ratio in the second step is preferably in the range of 1.1 to 25 times, more preferably in the range of 1.2 to 10 times, and still more preferably in the range of 1.3 to 5 times. Within range. When the draw ratio is lower than 1.1 times, the degree of improvement in flexibility is small, and when the draw ratio is higher than 25 times, the effect of increasing the draw ratio is reduced. There is a tendency for breakage to occur easily.

  The stretching speed in the second step is preferably in the range of 10 to 20000% / min, and more preferably in the range of 100 to 10000% / min. If the stretching speed is slower than 10% / min, it takes time to perform stretching, resulting in an increase in production cost. If the stretching speed is faster than 20000% / min, the stretched film may be broken.

  Moreover, in the said extending | stretching method, it is preferable that the draw ratio of the 2nd step is larger than the draw ratio of the 1st step. If the draw ratio in the first step is equal to or higher than the draw ratio in the second step, it may be difficult to achieve both flexibility and a necessary retardation value for an arbitrary axis.

  In the said extending | stretching method, it is preferable to extend | stretch in the direction orthogonal to the extending | stretching direction of the 1st step at the 2nd step. In this case, the flexibility with respect to the bending of an arbitrary shaft can be sufficiently provided.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these. Hereinafter, for convenience, “part by weight” may be simply referred to as “part”, and “liter” may be simply referred to as “L”.

In the following description, the following abbreviations MMA: methyl methacrylate MHMA: 2- (hydroxymethyl) methyl acrylate BzMA: benzyl methacrylate MIBK: methyl isobutyl ketone MEK: methyl ethyl ketone EDTA: disodium ethylenediaminetetraacetate SFS: sodium formaldehyde sulfo Xylate BA: n-butyl acrylate St: styrene BDMA: 1,4-butanediol dimethacrylate AMA: allyl methacrylate PBH: t-butyl hydroperoxide AN: acrylonitrile may be used.

<Polymerization reaction rate, polymer composition analysis>
The reaction rate during the polymerization reaction and the content of the specific monomer unit in the polymer were determined by gas chromatography (manufactured by Shimadzu Corporation, apparatus name: GC17A) based on the amount of unreacted monomer in the obtained polymerization reaction mixture. ) And measured.

<Content of BzMA structural unit>
^It calculated | required by measuring by <1> H-NMR (Product name: FT-NMR UNITY plus400, 400MHz, the Varian company make, solvent: gun chloroform, an internal standard substance: mesitylene).

<Dynamic TG>
The polymer (or polymer solution or pellet) is once dissolved or diluted in tetrahydrofuran, poured into excess hexane or methanol for reprecipitation, and the taken out precipitate is vacuum dried (1 mmHg (1.33 hPa), 80 ° C. Volatile components and the like were removed by conducting the reaction for 3 hours or more, and the obtained white solid resin was analyzed by the following method (dynamic TG method).

Measuring apparatus: Thermo Plus2 TG-8120 Dynamic TG (manufactured by Rigaku Corporation)
Measurement conditions: Sample amount 5 to 10 mg
Temperature increase rate: 10 ° C / min
Atmosphere: Nitrogen flow 200ml / min
Method: Step-like isothermal control method (controlled at a weight reduction rate value of 0.005% / sec or less between 60 ° C and 500 ° C)
<Dealcoholization reaction rate (lactone cyclization rate)>
The dealcoholization reaction rate (lactone cyclization rate) is based on the weight loss that occurs when all hydroxyl groups are dealcoholated as methanol from the polymer composition obtained by polymerization, before the weight reduction starts in dynamic TG measurement. It calculated | required from the weight reduction by the dealcoholization reaction from 150 degreeC to 300 degreeC before decomposition | disassembly of a polymer starts.

That is, in the dynamic TG measurement of the polymer having a lactone ring structure, the weight reduction rate between 150 ° C. and 300 ° C. is measured, and the obtained actual weight reduction rate is defined as (X). On the other hand, from the composition of the polymer, all the hydroxyl groups contained in the polymer composition are involved in the formation of the lactone ring, so that it becomes an alcohol and is dealcoholized. (Y) is the weight loss rate calculated on the assumption that the% dealcoholization reaction has occurred. The theoretical weight reduction rate (Y) is more specifically the molar ratio of raw material monomers having a structure (hydroxyl group) involved in the dealcoholization reaction in the polymer, that is, the raw material unit in the polymer composition. It can be calculated from the content of the monomer. These values (X, Y) are calculated from the dealcoholization formula:
1- (actual weight reduction rate (X) / theoretical weight reduction rate (Y))
Substituting into, the value is obtained and expressed in% to obtain the dealcoholization reaction rate.

  As an example, the proportion of the lactone ring structure in the pellets obtained in Production Example 2 described later is calculated. When the theoretical weight loss rate (Y) of this polymer was determined, the molecular weight of methanol was 32, the molecular weight of methyl 2- (hydroxymethyl) acrylate was 116, and methyl 2- (hydroxymethyl) acrylate. Since the content (weight ratio) in the polymer before lactone cyclization is 29.7% by weight in terms of composition, (32/116) × 29.7≈8.19% by weight. On the other hand, the actual weight loss rate (X) by dynamic TG measurement was 0.25% by weight. When these values are applied to the above-described dealcoholization calculation formula, 1− (0.25 / 8.19) ≈0.969 is obtained, so that the dealcoholization reaction rate is 96.9%.

Then, assuming that the lactone cyclization reaction was performed by the amount corresponding to the dealcoholization reaction rate, the content ratio (wt%) of the following formula lactone ring = B × A × M _R / M _m
(Wherein, B is in the lactone cyclization preceding polymers, the weight proportion of the raw material monomer structural units having the structure (hydroxyl group) responsible for the lactonization, M _R lactone ring structure units to produce M _m is the molecular weight of the raw material monomer having a structure (hydroxyl group) involved in lactone cyclization, and A is the dealcoholization reaction rate)
Thus, the lactone ring content ratio can be calculated.

  For example, in the case of Production Example 2, the content of methyl 2- (hydroxymethyl) acrylate in the polymer before lactone cyclization of the acrylic resin (pellet (P-1)) was 29.7% by weight, and the calculated desorption. Since the formula amount of the lactone ring structural unit generated when methyl 2- (hydroxymethyl) acrylate having an alcohol reaction rate of 96.9% and a molecular weight of 116 is condensed with methyl methacrylate is 170, an acrylic resin The content ratio of the lactone ring in is 42.2 (≈29.7 × 0.969 × 170/116) wt%.

<Weight average molecular weight>
The weight average molecular weight of the polymer was determined by polystyrene conversion of GPC (GPC system manufactured by Tosoh Corporation, chloroform solvent).

<Thermal analysis of resin and film>
The thermal analysis of the resin and the film was performed using a DSC (manufactured by Rigaku Corporation, apparatus name: DSC-8230) under conditions of a sample of about 10 mg, a heating rate of 10 ° C./min, and a nitrogen flow of 50 cc / min. . The glass transition temperature (Tg) was determined by the midpoint method according to ASTM-D-3418. In addition, the measurement of the said glass transition temperature was performed in the temperature range of 30-250 degreeC.

<Melt flow rate>
The melt flow rate was measured at a test temperature of 240 ° C. and a load of 10 kg based on JIS K7210.

<Optical characteristics>
The retardation value (Re) in the film plane and the retardation value (Rth) in the thickness direction at a wavelength of 589 nm were measured using KOBRA-WR manufactured by Oji Scientific Instruments. Select the incident angle dependency (single N calculation) as the measurement item, enter the average refractive index of the film measured with an Abbe refractometer, the film thickness d, the slow axis as the tilt central axis, and the incident angle as 40 °, In-plane retardation value (Re) and thickness direction retardation value (Rth), retardation value measured by tilting the slow axis by 40 ° (Re (40 °)), three-dimensional refractive index nx , Ny and nz were obtained.

  The total light transmittance and haze were measured using NDH-1001DP manufactured by Nippon Denshoku Industries Co., Ltd. The refractive index was measured in accordance with JIS K 7142 using a refractometer (manufactured by Atago Co., Ltd., apparatus name: Digital Abbe refractometer DR-M2) with respect to a measurement wavelength of 589 nm.

<Thickness of film>
Measurement was performed using a Digimatic Micrometer (manufactured by Mitutoyo Corporation).

<Folding resistance>
The number of folding times of the film was 15 mm in width, which was allowed to stand at 25 ° C. and 65% RH for 1 hour or longer using a folding resistance tester (manufactured by Tester Sangyo Co., Ltd., MIT, BE-201 type). Using a sample film having a length of 80 mm, measurement was performed in accordance with JIS P8115 under the condition of a load of 50 g. In addition, the measurement direction of the biaxially stretched film was folded in two orthogonal axial directions, and the number of times of folding was measured. Measurement was performed three times in each direction, the average value in each direction was determined, and the average value in the direction where the average value was small was taken as the number of folding times.

[Production Example 1]
In a 30 L reaction kettle equipped with a stirrer, temperature sensor, cooling pipe, nitrogen introducing pipe, 5200 g of methyl methacrylate (MMA), 2500 g of methyl 2- (hydroxymethyl) acrylate (MHMA), 2300 g of benzyl methacrylate (BzMA), 10000 g of toluene was charged. Next, the contents of the reaction kettle were heated to 105 ° C. while flowing nitrogen into the reaction kettle, and after starting refluxing, tertiary butyl peroxyisononanoate (trade names: Lupasol 570, Atofina Yoshitomi ( Co., Ltd.)) and simultaneously adding 6.0 g of t-amyl peroxyisononanoate and 100 g of toluene over 6 hours while adding dropwise an initiator solution under reflux (about 105 to 110 ° C.). Solution polymerization was performed. After the dropwise addition of the t-amyl peroxyisononanoate / toluene solution, aging was performed for another 2 hours.

  The reaction rate of the obtained polymer was 96.4%, the content of the MHMA structural unit in the polymer was 25.1% by weight, and the content of the BzMA structural unit was 23.2%.

  To the obtained polymer solution, 20 g of an octyl phosphate / dioctyl phosphate mixture (manufactured by Sakai Chemicals, trade name: Phoslex A-8) was added, and the cyclization condensation reaction was performed under reflux (about 80 to 105 ° C.) for 2 hours. Further, a cyclization condensation reaction was carried out at 240 ° C. for 1.5 hours under pressure (up to a gauge pressure of about 1.6 MPa) in an autoclave using a heating medium at 240 ° C.

  The polymer solution obtained by the above cyclization condensation reaction is a bent type screw having a barrel temperature of 250 ° C., a rotation speed of 100 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1, and a forevent number of 4. Introduced into a twin-screw extruder (φ = 29.75 mm, L / D = 30) at a processing rate of 2.0 kg / hour in terms of resin amount, cyclization condensation reaction and devolatilization are carried out in the extruder, A transparent pellet (P-1) was obtained by extrusion.

  When the obtained pellet (P-1) was measured for dynamic TG, a weight loss of 0.15% by weight was detected. Moreover, the weight average molecular weight of the pellet (P-1) was 150,000, the melt flow rate (MFR) was 20 g / 10 minutes, and the glass transition temperature (Tg) was 130 ° C. Moreover, content of the BzMA structural unit in a pellet (P-1) was 23.6 weight%, and the refractive index measured by producing a press film was 1.517.

[Production Example 2]
To a 30 L reaction kettle equipped with a stirrer, temperature sensor, cooling pipe, nitrogen introduction pipe, 7000 g of methyl methacrylate (MMA), 3000 g of methyl 2- (hydroxymethyl) acrylate (MHMA), methyl isobutyl ketone (MIBK) and methyl ethyl ketone 6667 g of a mixed solvent composed of (MEK) (weight ratio 9: 1) was charged, and the temperature was raised to 105 ° C. while refluxing nitrogen. When refluxed, tertiary butyl peroxyisononanoate (trade name) was used as an initiator. : Lupazole 570, manufactured by Atofina Yoshitomi Co., Ltd.) 6.0 g, and at the same time 12.0 g of tertiary butyl peroxyisononanoate and 3315 g of a mixed solvent composed of MIBK and MEK (weight ratio 9: 1) The resulting solution is added dropwise over about 3 hours under reflux (about 95-110 ) In carried out solution polymerization, it was aged over a period of 4 hours. The polymerization reaction rate was 94.5%, and the MHMA content (weight ratio) in the polymer was 29.7%.

  To the resulting polymer solution, 20 g of an octyl phosphate / dioctyl phosphate mixture (manufactured by Sakai Chemicals, trade name: Phoslex A-8) was added, and cyclization condensation reaction was performed under reflux (about 85 to 100 ° C.) for 2 hours. Further, a cyclization condensation reaction was carried out for 1.5 hours under pressure (gauge pressure up to about 2 MPa) in an autoclave using a heating medium at 240 ° C.

  Subsequently, the polymer solution obtained by the cyclization condensation reaction is subjected to cyclization condensation reaction and devolatilization in a bent type screw twin screw extruder in the same manner as in Production Example 1, and then extruded to obtain transparent pellets. (P-2) was obtained.

  When the obtained pellet (P-2) was measured for dynamic TG, a weight loss of 0.25% by weight was detected. The weight average molecular weight of the pellet (P-2) is 127,000, the melt flow rate is 6.5 g / 10 minutes, the glass transition temperature is 140 ° C., and the refractive index measured by producing a press film is It was 1.504.

[Production Example 3] (Production of elastic organic fine particles (G-1))
In a polymerization vessel equipped with a cooler and a stirrer, 120 parts of deionized water, 50 parts of butadiene rubber polymer latex (average particle size 240 nm) as a solid content, 1.5 parts of potassium oleate, sodium formaldehyde sulfoxy 0.6 parts of the rate (SFS) was added, and the inside of the polymerization vessel was sufficiently replaced with nitrogen gas.

  Subsequently, after the internal temperature was raised to 70 ° C., a mixed monomer solution consisting of 36.5 parts of styrene and 13.5 parts of acrylonitrile, 0.27 parts of cumene hydroxy peroxide, and 20.0 deionized water. Polymerization was carried out while continuously dropping the polymerization initiator solution consisting of parts over 2 hours. After completion of the dropwise addition, the internal temperature was raised to 80 ° C. and polymerization was continued for 2 hours. Next, after cooling to an internal temperature of 40 ° C., it was passed through a 300 mesh wire net to obtain an emulsion polymerization liquid of elastic organic fine particles.

  The obtained emulsion polymerization liquid of elastic organic fine particles is salted out with calcium chloride, coagulated, washed with water, and dried to obtain powdered elastic organic fine particles (G-1, average particle size: 0.260 μm, soft polymer layer). Of refractive index: 1.516).

  A particle size distribution measuring device (Submicron Particle Sizer NICOMP380) manufactured by NICOMP was used to measure the average particle size of the elastic organic fine particles.

  The “butadiene rubber polymer latex (average particle size 240 nm)” was produced by the following method. In a pressure-resistant reaction vessel, 70 parts of deionized water, 0.5 part of sodium pyrophosphate, 0.2 part of potassium oleate, 0.005 part of ferrous sulfate, 0.2 part of dextrose, p-menthane hydroperoxide A reaction mixture consisting of 1 part and 28 parts of 1,3-butadiene was added, the temperature was raised to 65 ° C., and polymerization was carried out for 2 hours. Next, 0.2 parts of p-hydroperoxide was added to the reaction mixture, and 72 parts of 1,3-butadiene, 1.33 parts of potassium oleate and 75 parts of deionized water were continuously added dropwise over 2 hours. The reaction was carried out for 21 hours from the start of polymerization to obtain the butadiene rubber polymer latex.

[Production Example 4] (Production of elastic organic fine particles (G-2))
In a polymerization vessel equipped with a cooler and a stirrer, 710 parts of deionized water and 1.5 parts of sodium lauryl sulfate were added and dissolved, and the internal temperature was raised to 70 ° C. Then, a mixed solution of 0.93 part of SFS, 0.001 part of ferrous sulfate, 0.003 part of EDTA, and 20 parts of deionized water was charged all at once into the polymerization vessel, and the inside of the polymerization vessel was sufficiently replaced with nitrogen gas.

  Monomer mixture (M-1) (BA 7.10 parts, St 2.86 parts, BDMA 0.02 parts, AMA 0.02 parts) and a polymerization initiator solution (PBH 0.13 parts, deionized water 10.0 parts). The polymerization vessel was added all at once and the polymerization reaction was carried out for 60 minutes.

  Subsequently, the monomer mixture (M-2) (BA 63.90 parts, St 25.20 parts, AMA 0.9 parts) and the polymerization initiator solution (PBH 0.246 parts, deionized water 20.0 parts) were separately prepared. Polymerization was performed while continuously dropping over 90 minutes. Polymerization was continued for another 60 minutes after the completion of the dropping. As a result, a core part of a core / shell structure of organic fine particles was obtained.

  Subsequently, the monomer mixed solution (M-3) (St 73.0 parts, AN 27.0 parts) and the polymerization initiator solution (PBH 0.27 parts, deionized water 20.0 parts) were continuously separated over 100 minutes. Polymerization was performed while dropping, and after completion of the dropping, the internal temperature was raised to 80 ° C. and polymerization was continued for 120 minutes. Next, after cooling to an internal temperature of 40 ° C., the mixture was passed through a 300 mesh wire net to obtain an emulsion polymerization liquid of organic fine particles.

  The obtained emulsion polymerization liquid of organic fine particles was salted out with calcium chloride, coagulated, washed with water and dried to obtain powdery organic fine particles (G-2, average particle size 0.105 μm).

[Production Example 5] (Production of elastic organic fine particle kneaded resin (B-1))
The pellet (P-1) obtained in Production Example 1 and the elastic organic fine particles (G-1) obtained in Production Example 3 were combined with a weight ratio of (P-1) / (G-1) = 70/30. While feeding using a feeder, the mixture was kneaded at 240 ° C. using a twin screw extruder having a cylinder diameter of 20 mm to obtain pellets (B-1).

[Production Examples 6 and 7] (Production of elastic organic fine particle kneaded resins (B-2) and (B-3))
Except that the type of pellet, the type of elastic organic fine particles, and the weight ratio of kneading were changed as shown in Table 1, the same operation as in Production Example 5 was performed, and pellet (B-1) and pellet (B-2) were obtained. I got each.

[Example 1]
The pellet (B-1) obtained in Production Example 5 was melt-kneaded using a single screw extruder having a 30 mmφ screw, and then extruded from a T-die having a width of 300 mm through a leaf disk polymer filter (filtration accuracy: 5 μm). Using a metal cast roll with a mirror surface and a flexible touch roll with a metal elastic outer cylinder that can be elastically deformed with a mirror surface, the film is formed so that both sides of the film are completely in contact with the roll at the same time. A film (FB1a) having a thickness of about 150 μm was produced.

  The obtained unstretched film (FB1a) was cut into a square having a side length of 97 mm and set on a chuck of a stretching machine so that the MD direction was the first stretching direction. The distance inside the chuck was 80 mm both vertically and horizontally. After preheating at 135 ° C. for 3 minutes, the first uniaxial stretching was performed in the MD direction at a stretching ratio of 1.5 times and a stretching speed of 240 mm / min. At this time, the width direction (direction perpendicular to the stretching direction) was not contracted.

  Subsequently, the second stretching was performed in the TD direction at a stretching ratio of 1.8 times and a stretching speed of 240 mm / min. At this time, as in the first-stage stretching, the width direction was prevented from shrinking. The results of the obtained stretched film are shown in Table 2.

[Example 2]
The same operation as in Example 1 was performed except that the temperature in stretching was changed to 140 ° C., the stretching ratio in the first stage was changed to 1.6 times, and the stretching ratio in the second stage was changed to 1.9 times. A stretched film was obtained. The results of the obtained biaxially stretched film are shown in Table 2.

Example 3
A biaxially stretched film was obtained in the same manner as in Example 1 except that the stretch ratio of the first stage was changed to 1.8 times and the stretch ratio of the second stage was changed to 2.1 times. The results of the obtained biaxially stretched film are shown in Table 2.

Example 4
A biaxially stretched film was obtained by performing the same operation as in Example 1 except that the pellet (B-1) obtained in Production Example 6 was changed to 137 ° C. It was. The results of the obtained biaxially stretched film are shown in Table 2.

Example 5
Except having changed the extending | stretching temperature to 125 degreeC, operation similar to Example 1 was performed and the biaxially stretched film was obtained. The results of the obtained biaxially stretched film are shown in Table 2.

Example 6
Example 1 except that the thickness of the unstretched film was 200 μm, the stretching temperature was 150 ° C., the first stage draw ratio was changed to 1.8 times, and the second stage draw ratio was changed to 2.2 times. Operation was performed to obtain a biaxially stretched film. The results of the obtained biaxially stretched film are shown in Table 2.

Example 7
Except that the pellet (B-1) was changed to the pellet (B-3) obtained in Production Example 7, the thickness of the unstretched film was changed to 230 μm, and the stretching temperature was changed to 143 ° C. Operation was performed to obtain a biaxially stretched film. The results of the obtained biaxially stretched film are shown in Table 2.

[Comparative Example 1]
The pellet (B-1) obtained in Production Example 5 was melt-kneaded using a single screw extruder having a 30 mmφ screw, and then extruded from a T-die having a width of 300 mm through a leaf disk polymer filter (filtration accuracy: 5 μm). Using a metal cast roll with a mirror surface and a flexible touch roll with a metal elastic outer cylinder that can be elastically deformed with a mirror surface, the film is formed so that both sides of the film are completely in contact with the roll at the same time. A film (FB1f) having a thickness of about 150 μm was produced.

  The obtained unstretched film (FB1f) was stretched using a corner stretch type biaxial stretching test apparatus X6-S (manufactured by Toyo Seiki Seisakusho). Specifically, first, the obtained unstretched film (FB1f) was cut into a rectangle having an MD direction of 97 mm and a TD direction of 80 mm, and set in a stretching machine so that the MD direction was the stretching direction. The chuck did not grip the film so that the TD direction could freely contract. The distance inside the chuck was 80 mm both vertically and horizontally. After preheating at 135 ° C. for 3 minutes, free end uniaxial stretching was performed in the MD direction at a stretching ratio of 2 and a stretching speed of 240 mm / min. Table 2 shows the measurement results of the obtained uniaxially stretched film.

[Comparative Example 2]
The same operation as in Comparative Example 1 was performed on the pellet (B-3) obtained in Production Example 7 except that the stretching temperature was changed to 143 ° C. to obtain a uniaxially stretched film. It was. Table 2 shows the results of the obtained uniaxially stretched film.

[Comparative Example 3]
The pellet (B-1) was tried to perform the same operation as in Example 1 except that the pellet (P-1) obtained in Production Example 1 was changed to a stretching temperature of 128 ° C. The film broke after the start. The same operation was tried once again, but the film broke during stretching. For this reason, a biaxially stretched film could not be obtained sequentially.

[Comparative Example 4]
A biaxially stretched film was obtained by performing the same operation as in Example 1 except that the pellet (B-1) obtained in Production Example 2 was changed to a pellet (P-2) at a stretching temperature of 160 ° C. . The results of the obtained biaxially stretched film are shown in Table 2.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The retardation film of the present invention has a retardation that is suitable for a retardation film and is very excellent in flexibility. For this reason, it can be used for the retardation film etc. which are used for the liquid crystal display device for VA (vertical alignment).

Claims (9)

A retardation film containing an acrylic polymer as a main component and elastic organic fine particles,
The in-plane retardation value at a wavelength of 589 nm is in the range of 15 nm to 100 nm,
The thickness direction retardation value at a wavelength of 589 nm is in the range of 70 nm to 400 nm,
A retardation film characterized by using a sample film having a width of 15 mm and a length of 80 mm and having a folding resistance of 100 or more measured in accordance with JIS P8115 under a load of 50 g.   The retardation film according to claim 1, wherein the folding resistance is 500 times or more.   The retardation film according to claim 1, wherein the haze is 2% or less.   The retardation film according to claim 1, which is obtained by biaxial stretching.   The elastic organic fine particle has a conjugated diene monomer structural unit constructed by polymerizing a conjugated diene monomer as an essential component, and has a glass transition temperature on the low temperature side of less than −40 ° C. The retardation film of any one of Claims 1-4.   The elastic organic fine particles have a conjugated diene monomer structure obtained by polymerizing at least one monomer selected from the group consisting of butadiene and isoprene. The retardation film of Claim 1.   The retardation film according to any one of claims 1 to 6, wherein the glass transition temperature on the high temperature side is within a range of 110 ° C or higher and 200 ° C or lower.   The retardation film according to claim 1, wherein the acrylic polymer has a lactone ring structure. The lactone ring structure is represented by the following general formula (1)

(In the formula, R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.)
The retardation film according to claim 8, which has a structure represented by: